1. Field of the Invention
The present invention relates in general to solid state image pickup device and in particular to a novel solid state image camera.
2. Description of the Prior Art
Prior art conventional solid state image pickup equipment uses a solid state image sensor comprising a charge transfer device such as a CCD which are arranged in a variety of configurations for use in moving image video cameras where incident light is irridated continuously on each photosensitive region of the image sensor and the output pickup signals are read out for each field or frame period so as to perform a successive imaging operation. In solid state image sensors where the signal charges obtained in the photosensitive regions are transferred smearing or blooming can occur because of the fact that some unrequired charges leak out to the transfer section or cause thermal excitation. This is a disadvantage of prior art solid state image pickup devices. In order to eliminate this disadvantage, solid state image sensors of the prior art have had overflow drains along the transfer section or are formed into a frame transfer type. Consequently, the prior art known solid state image sensors have become extremely complicated in structure in an attempt to eliminate smearing or blooming and very expensive and highly advanced techniques have had to be used in manufacturing semiconductors which has resulted in extremely high production cost.
It has been customary previously to utilize even for still image pickup mode use such extremely expensive solid state image sensors to form a pickup unit.
Generally, image sensors for use in a video camera to produce television signals are designed so as to provide spatially deviated pictures with respect to odd and even fields in conformity with the interlaced scanning utilized in a television receiver so that the video signals representing the individual fields are alternately read out. Accordingly, in a still image pickup mode, when using an image sensor which is equipped with photosensitive regions corresponding to one frame picture elements, there is a problem of flicker when obtaining a still frame image when picking up a moving object due to fluctuations which occur in the image between each fields since the video signals of the individual fields spatially vary from each other. So as to avoid this undesired phenomena formation of a still field picture according to the prior art has lead to extreme deterioration in the vertical resolution of the video signals.
Normally, the exposure time of an image sensor in a video camera to obtain television signals is set to be equal approximately to the period of one field. However, in a still image pickup unit it is desired that the shutter be controlled so as to vary the exposure time. For example, in order to obtain a distinct still image of an object in motion it is necessary to shorten the exposure time so as to prevent blur of the image which results from the motion of the object. Since varying the exposure time causes a variation in the amount of exposure of the image sensor it becomes necessary to obtain a pickup output signal of an adequate level from the image sensor to adjust the opening of the optical path of the incoming incident light or to provide a circuit to control the level of the pickup output signal.